Heretofore, there has been known continuous cast in which molten metal is supplied into a movable casting die formed by a roll and a belt, this molten metal is brought into contact with the casting die thereby to be cooled and solidified, and a casting material is continuously manufactured. As such the continuous cast, there is, for example, a twin roll method using a twin roll movable casting die composed of a pair of rolls. In this method, a pair of rolls which rotate in opposite directions to each other are arranged opposed to each other, and molten metal is poured between the rolls thereby to obtain a casting material. This twin-roll method is used generally in manufacture of sheet materials of pure aluminum and aluminum alloy. As a nozzle which supplies the molten metal between the rolls, a nozzle formed of thermal insulation material such as aluminum or silica has been known (refer to, for example, Patent Document 1)
On the other hand, Mg is smaller in specific gravity (density g/cm3, 20° C.: 1.74) than the above Al, and is the most lightweight of metal materials used for structure. Therefore, as a material in various fields where weight reduction is required, great expectations are harbored on magnesium alloy having pure magnesium or Mg as a main component. For example, manufacture of a casting material by continuous cast as a magnesium alloy material has been described in Patent Document 2.    Patent Document 1: JP-A-11-226702    Patent Document 2: International Publication No. 02/083341 pamphlet